Among the most ubiquitous effects of addictive drugs, but the least well studied, is drug craving. There has not even existed a validated psychometric instrument for the evaluation of craving that would lend itself to the systematic development of medications for treating drug craving. We have recently developed such instrumentation for cocaine, heroin, alcohol, marijuana, and tobacco. This research should help us to identify mechanisms of addiction that are common across drug classes and therefore lead to a better understanding of the mechanisms that underlie drug craving. Our initial findings indicated that craving for cocaine and heroin is a multidimensional construct, involving an admixture of urges and desire, intent to use, loss of control over use, and anticipation of positive outcome. Subject testing has been completed with the Alcohol Craving Questionnaire, Marijuana Craving Questionnaire, and Tobacco Craving Questionnaire. Recently, we have been manipulating tobacco and marijuana craving in the laboratory. Using narrative scripts that either contain explicit descriptors of tobacco or marijuana craving or scripts that contain no craving descriptors, we have shown that tobacco and marijuana craving can be manipulated in a drug-abusing population and that craving can vary along a continuum. Craving is also associated with negative mood states. We also found that craving for tobacco was positively correlated with craving for other drugs of abuse, suggesting that situations that trigger tobacco craving can also elicit drug craving. We have recently begun a study to investigate the effect of tobacco craving on memory encoding and retrieval. Preliminary results sugggest that encoding is more easily disrupted by craving than retrieval of information from memory. These advances in instrument development and enhanced understanding of craving should enable more rapid progress in the ability to produce more selective and effective medications and other interventions to meet the needs of those addicted to drugs. With these instruments we should be able to predict which craving dimensions may be relieved by medications and which will require other intervention to enable the person to achieve and sustain drug abstinence.